The present invention relates to a method and apparatus for an integrated RAM thermal sensor and, more particularly, to a method and apparatus for thermal sensing and regulating in RAM devices.
As the frequency of access to a device increases, the device generates heat. The heat generated has to be removed from the device to guarantee data integrity and long term device reliability.
Attempts have been made to address the heating problems. For example, external thermal sensors to detect when the device gets too hot and accordingly suspend or slow down access have been used. Separate chips or circuits that act as a thermal sensor have been used to detect the temperature of the RAM device but several problems exist with this approach. One problem is that the sensor will typically be several generations of technology behind the more frequently updated RAM devices and other chips on the motherboard. This usually means that the more modern chips are operating at a lower voltage. Therefore, the thermal sensor will need a separate voltage feed, apart from the other chips, which is cumbersome, especially when the trend is towards miniaturization. Another problem is that the external sensor is much less accurate because it is measuring the temperature through a medium connected to or touching the device being measured. Typical mediums can be a wire or a metallic plate. The medium has some resistance and accordingly the heat will dissipate to some degree before being measured. Finally, by having external circuitry for temperature sensing along with interconnections to and from the circuitry, additional failure points are introduced into the system. For example, the IC housing the external sensor may come lose from its socket while the memory device may be fine. These problems may prevent an external temperature sensor from adequately protecting the RAM devices from overheating.
Another approach known in the field has been to implement a counter, usually external to the RAM device, which keeps track of the number of accesses within a certain time period. If the number exceeds a certain threshold then it is assumed that the device is nearing its heat limit. One problem with this approach is that the initial condition for the temperature must be assumed. For example, if someone left a laptop computer in a parked car on a hot day, the starting temperature will be much higher than normal. Therefore, the counter will not work properly because it will still assume the device can handle the same number of accesses as if it started at a normal temperature. Another problem is that the temperature is dependent on other variables aside from the data access frequency. One such variable is the type of chassis. Therefore, this mechanism must be used in light of the worst-case scenario of chassis heating, which will often yield erroneous temperature readings.
According to an embodiment of the present invention, a method and apparatus for thermal sensing and regulating in a RAM device is provided. An analog signal is created by passing a predetermined voltage through a temperature sensitive diode embedded in the RAM device. The analog signal is converted to digital temperature data, and the digital temperature data-is then transmited to a controller host capable of regulating an access rate of the RAM device.